Okabe Mayuko, Tsukahara Yuko, Tanaka Minoru, Suzuki Kaori, Saito Shigeru, Kamiya Yoshiko, Tsujimura Tohru, Nakamura Koji, Miyajima Atsushi
Laboratory of Cell Growth and Differentiation, Institute of Molecular and Cellular Biosciences, The University of Tokyo, Tokyo 113-0032, Japan.
Development. 2009 Jun;136(11):1951-60. doi: 10.1242/dev.031369.
Hepatic oval cells are considered to be facultative hepatic stem cells (HSCs) that differentiate into hepatocytes and cholangiocytes in severely injured liver. Hepatic oval cells have also been implicated in tumorigenesis. However, their nature and origin remain elusive. To isolate and characterize mouse oval cells, we searched for cell surface molecules expressed on oval cells and analyzed their nature at the single-cell level by flow cytometric analysis and in the in vitro colony formation assay. We demonstrate that epithelial cell adhesion molecule (EpCAM) is expressed in both mouse normal cholangiocytes and oval cells, whereas its related protein, TROP2, is expressed exclusively in oval cells, establishing TROP2 as a novel marker to distinguish oval cells from normal cholangiocytes. EpCAM(+) cells isolated from injured liver proliferate to form colonies in vitro, and the clonally expanded cells differentiate into hepatocytes and cholangiocytes, suggesting that the oval cell fraction contains potential HSCs. Interestingly, such cells with HSC characteristics exist among EpCAM(+) cells of normal liver. Intriguingly, comparison of the colony formation of EpCAM(+) cells in normal and injured liver reveals little difference in the number of potential HSCs, strongly suggesting that most proliferating mouse oval cells represent transit-amplifying cells rather than HSCs.
肝卵圆细胞被认为是兼性肝干细胞（HSCs），在严重损伤的肝脏中可分化为肝细胞和胆管细胞。肝卵圆细胞也与肿瘤发生有关。然而，它们的性质和起源仍然不清楚。为了分离和鉴定小鼠卵圆细胞，我们寻找在卵圆细胞上表达的细胞表面分子，并通过流式细胞术分析和体外集落形成试验在单细胞水平上分析它们的性质。我们证明上皮细胞粘附分子（EpCAM）在小鼠正常胆管细胞和卵圆细胞中均有表达，而其相关蛋白TROP2仅在卵圆细胞中表达，从而确立了TROP2作为区分卵圆细胞与正常胆管细胞的新型标志物。从损伤肝脏中分离出的EpCAM(+)细胞在体外增殖形成集落，克隆扩增的细胞分化为肝细胞和胆管细胞，这表明卵圆细胞部分含有潜在的肝干细胞。有趣的是，在正常肝脏的EpCAM(+)细胞中也存在具有肝干细胞特征的此类细胞。耐人寻味的是，正常肝脏和损伤肝脏中EpCAM(+)细胞集落形成的比较显示，潜在肝干细胞的数量几乎没有差异，这强烈表明大多数增殖的小鼠卵圆细胞代表过渡放大细胞而非肝干细胞。
